#include <iostream>
#include <iomanip>
#include <math.h>

using namespace std;

int main(int argc, char* argv[])
{
	const double pi = 3.141592653589793;
	double x1, y1, x2, y2, x3, y3;
	while (cin>>x1>>y1>>x2>>y2>>x3>>y3)
	{
		double diameter, circum;
		double a, b, c;
		double sin, cos;

		a = sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1));
		b = sqrt((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2));
		c = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
		cos = ((x3 - x2) * (x1 - x2) + (y3 - y2) * (y1 - y2)) / (b * c);
		sin = sqrt(1 - cos * cos);
		diameter = a / sin;
		circum = diameter * pi;
		cout << setiosflags(ios::fixed) << setprecision(2);
		cout<<circum<<endl;
	}
	return 0;
}